Circuit breaker testing apparatus



Jun 30, 1942. w F SKEATS 2,288,331

CIRCUIT BREAKER TESTING APPARATUS Filed Aug. 13, 1940 4 .22 h 2Inventor: Wilfred F. Slmaaig His Attorn Patented June 30, 1942 UNITEDSTATES PATENT OFFICE cmcurr BREAKER. TESTING APPARATUS Wilfred F.Skeats, Lansdowne, Pa., assignor to General Electric Company, acorporation of New York Application August 13, 1940,Serial No. 352,392

14 Claims.

improved, simply operating, synthetic circuit for testing circuitbreakers under conditions simulating the conditions of short circuit atrated apparent power as they occur in actual operation.

It is another object of my invention to provide an improved arrangementfor testing circuit breakers in which the recovery voltage is built upwith great rapidity after current zero in the test breaker.

It is a further object of my invention to provide improved apparatus ofthe foregoing character having a simple arrangement which determinesvery promptly and accurately when current zero in the test breaker hasoccurred and which automatically synchronizes with this current zero theapplication to the test breaker of a voltage surge simulating a recoveryvoltage transient as the circuit interrupting device being tested isopened.

Other objects and advantages of my invention will become apparent as thedescription proceeds.

ment is such that both circuit breaker units clear together or such thatthe tested breaker clears slightly earlier so that itwill be subjectedto the full recovery voltage while clearing its current.

The foregoing arrangement may be modified by connecting an inductance inthe circuit between one terminal of the high current power source andthe auxiliary breaker or between the auxiliary breaker and the breakerunder test. A further modification may be made by connecting anauxiliary resistance element in series circuit relation with a spark-gapacross the terminals of the breaker under test. The inductance elementaids in rapid extinction of the residual current flowing through theauxiliary breaker after current zero in the test breaker so that thebuild-up of voltage at the point between the two breakers is not undulydelayed. The insertion of the resistance element and the sparkgapprovides the desired overshoot, as will be explained hereinafter.

The invention will be understood more readily from the followingdetailed description when considered in connection with the accompanyingdrawing and those features of the invention which are believed to benovel and patentable are pointed out in the appended claims;- In thedrawing Fig. 1 is a circuit diagram representing schematically oneembodiment of my invention, and Figs. 2 and 3 are modified circuitdiagrams of embodiments of my invention.

Referring now to Fig. 1, I have shown schematically a currentinterrupting device or a circuit breaker unit H which is to betested-connested in series with an auxiliary interrupting device orcircuit breaker unit I! across a suitable high current source, such as agenerator in the form of an alternator I 3. If desired, a threepoleswitch I 4 may be employed, two poles of which are interposed betweenthe alternator I3 and the two circuit breakers. Ordinarily, it isdesirable that the circuit breaker units II and H be similar for reasonswhich hereinafter appear. The current source [3 is of such capacity asto supply the full current at which it is desired to test the breaker.It will be understood that circuit interrupting devices, such as II andI2, are ordinarily provided with operating mechanisms which areelectrically controlled and the same control means for use in protectingelectrical circuits under commercial use of circuit breakers are usedfor causing the circuit breakers H and 12 to open as soon as the shortcircuit is produced.

4 These arrangements, however, are well known to those skilled in theart, are not a part oi. my invention, and, therefore, are omitted forthe sake of simplicity in the description and drawing.

In order that thedevice I I may be tested under conditions simulatingactual operating conditions with a high recovery voltage, I provide ahigh voltage at point IT. This voltage is connected to the test breakerterminals I9 and 20 through a series impedance 2| which in this instancecomprises a resistance element. For reasons of safety and to provide afixed reference point, the points i6, 20 and I8 are grounded at 24. Thevoltage applied to the high potential terminal II should be of such aphase relation that it is near its crest value at the time of currentzero in the high current circuit which includes the test breaker II. Inother words, the voltage across the terminals l1 and [8 should lead thecurrent flowing through the breaker H by approximately degrees, sincethis is the approximate phase in the art and a more detailed descriptionor illustration thereof is regarded as unnecessary. In Fig. 2, I haveshown a modification in which a resistance element It and a spark-gap 31are considerations being that it be a voltage source of correct phaseangle and of low regulation to the load imposed by the impedance element2|.

However, because of the convenience and simplicity made possible, Iprefer to supply the high voltage from the polyphase alternator II whichis employed for sending the high current through the two breakers.

It will be appreciated that the normal frequency recovery voltage isrelatively high in comparison with the voltage which might be obtaineddirectly from the phases of the alternator 13 which are connected to thecircuit terminals l5 and It. In order to produce such a recovery voltagewithout drawing appreciable power from the alternator II, I employ astep-up transformer having a primary winding 26 and a secondary winding21. The primary winding 26 is connected to the ground connection 24 andterminal l8 and to the unused terminal 28, these terminals beingconnected respectively to one: of the used phases and the unused phaseof the alternator I! through the breaker I4. I wish to point out that anautotransformer may be employed instead of the transformer 25, ifdesired. As explained hereinbefore it is desired that the high voltagesupplied to the breaker under test shall be' near its crest value at thetime of current zero in the test breaker. To this end I provide a phaseshifting device comprising preferably a resistor 29 and a capacitor 30which are connected in series circuit relation across the high potentialwinding 21. The simulated recovery voltage is obtained by connecting thehigh side terminal l1 and the grounded terminal I. acros the capacitor'30. By properly corrdinating the sizes of the resistor 29 and thecapacitor 30 in conjunction with the transformer 25 the voltage acrossthe capacitor may be made to lead the current through the breaker II byapproximately 90 degrees.

It will be understood that for obtaining records of tests on anoscillograph 3| suitable oscillograph attachments are provided, such asa current shunt or a transformer 32 in series with the breaker elements,a potential transformer element 33 connected across the breakerterminals l9 and 20, and a second shunt or current transformer 34connected in the circuit of the breaker II under test and the capacitorelement 30.

Also, in general it may be found very useful, if not absolutelynecessary, to employ a cathode ray oscillograph for examining thebehavior of the voltage at the high voltage terminal of the connected inseries circuit relation across the breaker terminals l9 and 20. Also, aninductance element 38 is connected between the terminal I! of thealternator l3 and the generator side of the auxiliary breaker l2. Thislatter element may also be employed in the arrangement of Fig. 1.

In Fig. 3, I have shown a further modification ,of Figs. 1 and 2whichincludes the inductance element 38 of Fig. 2 and in which the resistanceelement 3' and spark-gap 31 of Fig. 2 are omitted. and the function ofthese latter elements performed by including in the impedance element aninductance I! in addition to a resistance element 2|. The inductanceelement 39 is located between the auxiliary breaker unit and the unitunder test, and in the illustrated embodiment it is shown connectedbetween the auxiliary unit and point l9.

The primary considerations governing the nature of the impedance elementconnected between points I! and I! of the several figures are first,that the voltage at point ll should be near its crest value at the timeof current zero in the high current circuit which includes the testbreaker, and second, that in order to obtain a high recovery rate afinite current should be flowing through this impedance element at thetime of current zero in the high current circuit. These considerationsare best met if this element is a pure resistance as shown in Fig. l,but the deleterious effect of a moderate deviation from this condition,as by the introduction of a small amount of reactance will be relativelyvery small.

When testing the interrupting ability of the circuit breaker ll, bothbreakers II and I 2 are first closed. Consider now the operation of thesystem as illustrated in Fig. 1 for applying to the test breaker arecovery voltage immediately after a current zero. Current of thedesired magnitude is applied from the alternator I! to the auxiliarybreaker l2 and the test breaker H. in series by closing the breaker H.At the same time an alternating voltage is supplied from the alternatorl3 or any other suitable auxiliary source to the primary winding 26 ofthe transformer 25. The application of power to the auxiliarytransformer sets up a voltage at point ll which by manipulation of thecircuit can be made to have any desired phase relation with respect tothe current through the breakers H and i2. If the current through thebreakers II and I2 has no direct current component the most severebreaker under test. Thus I have shown -a suitable potentiometer 33a forconnecting the defleeting plates of such an oscillograph to the testbreaker. There may also be provided an attachment for recording motionof the breaker mechanism or contacts and possible attachments forrecording other conditions. Such oscillographs and attachments, however,do not constitute a part of my invention and relate to recording theresults of the test rather than to the arrangement or method ofsubjecting the breaker to the test. Furthermore, such osciliographs andattachments are well known to those skilled conditions will usually beobtained when the voltage at H leads the current through the breakers bydegrees so that the voltage crest occurs at current zero of the testbreaker. In some cases it may be found desirable to increase the currentthrough the breakers by the employment of a displaced wave rather than asymmetrical wave and in such event it may still 'be desired that thevoltage be at its crest value at the time of current zero. This may bebrought about for the current zero after the major loop by reducingsomewhat the angle of lead of the voltage at point ll.

While there is voltage at point l1 and the breakers II and I2 are stillclosed and even after the breaker contacts have been separated by theoperating mechanism, up to the time that the are drawn between theopening contacts is broken and the current reduced to zero, the

' breakers.

' zero is reached. with the current through the resistance 2| leadingthe breaker current, upon opening of the breakers, the current throughthe test breaker will reach zero a short time before the current throughthe auxiliary breaker, the current through the auxiliary breaker at thistime being equal to the instantaneous value of the current through theresistance II. This current is so low that in many cases it may beexpectedcto be easily and promptly extinguished in the auxiliary breakerarc. When this occurs the entire current through the resistance 2i,having no other place to flow, flows into the small stray capacitance ofthe circuit connection I! between the auxiliary breaker and the testbreaker. to raise very rapidly the voltage at the common point I!between the two breakers until that voltage becomes substantially equalto the voltage of the capacitor 30 corresponding to the voltage at thepoint I1, the rate of this rise in voltage being governed by themagnitude of the resitsance 2| and the capacitance of the point betweenthe two breakers, together with some effect from the characteristics ofthe current circuit which will be explained hereinafter. From that timeon the voltage at the point l9 between the two breakers remains equal tothe voltage at H except for the drop in potential across the resistance2i, usually negligible, which will be caused by the' charging currentfor the stray capacitance of the connection between the two breakers.When this voltage'has been maintained in this way for two or threecycles the test may be considered complete.

From the foregoing description of the operation it will be noted thatthe test breaker II has sufferedthe passage of a high current which itinterrupted by an arc and that very promptly after this interruption thevoltage across the test breaker rose rapidly to the voltage at the pointI I thereafter being maintained at the voltage of point I! until thecompletion of the test. This is rather a good approximation of the dutyof the breaker I I in a normal interruption of the current whichinitially flowed through it at a circuit voltage equal to that at pointl1. However, it may fall short of this in two respects. The residualcurrent which was spoken of as flowing through the auxiliary breaker I2after current zero in the test breaker II may not be extinguished asrapidly as desired. Such a condition will delay the build-up of voltageat the point I9 between the two breakers and consequently reduce theseverity of the test. Also, in the interruption of many circuits thevoltage across the breaker rises during the transient immediatelyfollowing interruption to an instantaneous value which may beapproximately twice as high as the normal crest value of applied voltageacross the breaker. .This rise above the crest value of applied voltageis referred to here- This current then starts immediately in asovershoot. The circuit as described in connection with Fig. 1 does notinclude features providing for such a rise or overshoot. It is to meetsuch conditions as the foregoing that the arrangements of Figs. 2'and 3have been devised.

In the apparatus of Figs. 1, 2 and 3, just before current zero, forproper polarity relationship, the

- polarity of the voltage at the capacitor 30 should be opposite to thatof the current flowing through.

the test breaker, by virtue of the fact that in the latter part of aloop of current in an inductive circuit the voltage is of oppositepolarity to the current which it produces. This being so, and thevoltage across the capacitor 30 and at point II being higher than thevoltage at I3, current will tend to flow through the auxiliary breakerafter interruption in the same direction which it has been flowingduring the last half cycle. This may mean that the current in theauxiliary breaker will be reduced almost to zero and then continue at alow value without reaching zero for about a quarter of a cycle. If thisoccurs, the voltage at the point I9 between the two breakers will bedissipated by conduction through the auxiliary breaker and only normalgenerator voltage will appear at this point. This state of ail'airs maycontinue fora good' fraction of a cycle, or, as I have found in somecases, it may continue only for a number of microseconds, the currentinthe auxiliary breaker eventually going out of its own accord. In thelatter situation, although the voltage at the point I9 between the twobreakers eventually does reach its proper value, there is some delay inits rise, so that even this conditionis prejudicial to thetruesignificance of the test. I

The foregoing situation may be controlled by causing the voltage on thegenerator side of the auxiliary breaker, as represented by theconnection 35, to rise initially at a rate approximately equal to thatat which it is desired to have the voltage rise at the point I9 betweenthe two breakers. If the voltage on the generator side 35 catches upwith the voltage on the other side I 9 of the auxiliary breaker for abrief instant during the rising period, the current through theauxiliary breaker will automatically be reduced to zero at this time andwill, therefore. have a very good chance of becoming extinguishedpermanently. It may not be necessary, however, to cause the voltage onthe generator'side of the auxiliary breaker to catchup completely withthe voltage at point I9 between the two breakers,

as merely reducing the current flow and the voltage across the auxiliarybreaker to a low value will tend to cause the arc in the auxiliarybreaker to become extinguished of its own accord.

It is for the purpose of causing the voltage to rise rapidly on thegenerator side of the auxiliary breaker that I introduce in thearrangement of Fig. 2 the inductance element 38 in the connection 35between the generator or alternator I3 and the auxiliary breaker elementI2, the inductance element being so located that the capacitance toground of the connection 35 between the auxiliary breaker and theinductance will be as low as possible.

A complete description of the arrangement of Fig. 2 is unnecessary for afull understanding of the invention in view of the foregoing descriptionof the operation of Fi 1.- The circuit of Fig. it behaves in the sameway as that of Fig. 1 up to the time when the current reaches zero inthe test breaker I I and the first difierence is with reference to theresidual current through the auxiliary breaker II. On account of thereactance supplied by the inductive reactance element 38 the major 'partof this residual current must flow into the capacitance to ground of thecircuit connection 35 between the auxiliary breaker and the reactorelement 38. Current will also tend to flow to this point through thereactor element, and the polarity of these two currents will be suchthat their effect in increasing the voltage to ground at connection 35will be additive. Thus, .the voltage at this point or at the generatorside of the auxiliary breaker rises rapidly and, in order to maintaincurrent flow through the auxiliary breaker 12, the voltage at the pointl5 between the two breakers must also rise rapidly so that the straycapacitance from this point to ground will draw a relatively highcurrent. This will drain some and perhaps all of the current through theauxiliary breaker l2, thu assuring prompt interruption whether thiscurrent zero can be attained before the voltage difference across thereactance 38 is reduced to zero. A mathematical analysis indicates thatthis can be done if the following equations are satisfied:

where i=current through impedance element between points" and l9.

- E=instantaneous generated voltage in high ourof this residual current.The possibility of the delay in the build-up of voltage across the testbreaker ll after current zero which was mentioned as a shortcoming ofthe circuit of Fig. 1 is thus eliminated in the arrangement of Fig. 2.

The reactance element 38 will also be efiective for bringing the currentthrough the auxiliary breaker to zero immediately after extinction ofthe arc in the breaker ll if it is placed between auxiliary breaker "andthe point I 9 as shown in the alternative arrangement of Fig. 3. The

action of this elementwhen so located may be mined by the voltage at ITand the impedance between points l1 and I9, and inasmuch as neither ofthese is subject to rapid change, this current will be substantiallyconstant over a period of microseconds. At the instant of current zeroin unit II, a current substantially equal to that flowing from I! to IDwill be flowing from H) through the reactance 38. This current is inopposition to the voltage across that circuit, and sincethe circuitconsists primarily of an inductance this current will be subject torapid decay and eventual reversal involving passage through zero at thetime of reversal which will provide an opportunity for are extinction inthe breaker unit I2. It will be obvious, however, that this changein thecurrent through reactor 38 must be accompanied by a rise in voltage at Hand consequently a reduction in voltage across the .unit 38. Indeed thevoltage at I 9 is normally expected to rise eventually to a value equalto that at I! which is considerably higher than that at breaker l2. Atthis time, unless the arc in breaker "has been extinguished so that ahigh potential difierence can be maintained across the contacts ofbreaker II, the voltage across thereactance unit 38 will have reversed.If this is allowed to occur, the inductance 38 can no longer be reliedupon to bring the current through the unit I! to zero. v

I am thus confronted with a situation which is initially favorable toproducing a current zero in the breaker unit I 2, but which is rapidlychanging in adverse manner,- and the question is rent source.C=effective stray capacitance at point l9. L0=inductance of high currentsource. L=inductance of reactor 38.

The foregoing is a slightly less exacting condition under mostcircumstances than that involved in bringing about current zero in thebreaker unit It with the inductance 38 located between the high currentsource and the auxiliary breaker unit I 2.

As stated hereinbefore, a second short-coming of the simple circuit ofFig. 1 is that it provides no overshoot, as do circuits commonlyencountered in practice, that is, upon interruption of the circuit theinstantaneous value of the recovery voltage does not exceed the crestvalue of the applied voltage. It is to meet this condition that I haveprovided in the arrangement of Fig. 2, the resistance element 38 whichis connected from the point l9 between the two breakers through thesphere-gap 31 to ground.' In this arrangement, the voltage across thecapacitor 30 and at the point I! is set slightly higher than the crestvalue of the recovery transient for which it is desired to test, and thesphere-gap 31 is set to break down at the crest value of the recoverycharacteristic.

Taking up the operation from the point at which the arcs in the twobreaker units have been extinguished, then, the voltage at the point l9between the two breakers rises along an exponential curve approachingthe voltage of capacitor 30 corresponding to the voltage at point l1.Before this voltage is quite attained, however, the sphere-gap 31 breaksdown, and the voltage at the point I9 between the two breakers fallsexponentially to a value determined by the relative magnitudes of theresistances 2| and 36. From that time on this voltage will maintain itsproper ratio to the capacitor voltage as the lat ter goes through itscyclic variations. It will thus be seen that the two resistances 2| and36 act as a potentiometer, maintaining the voltage at the point I 9between the two breakers equal to some fraction of the voltage at pointI! rather than equal to the voltage at IT itself. If the voltage at I!is made enough in excess of that for which it is desired to test thebreaker H to compensate for the reduction of voltage in thepotentiometer, the result will be a. test at the voltage finallymaintained at the point Is between the two breakers with an overshootcorresponding to that allowed by' the sphere-gap. Thus the overshootwhich was lacking in the circuit of Fig. 1 has been supplied.

It has been stated hereinbefore that the primary factors determining thecharacter of the impedance element which is connected between the pointsH and 19 are the desirability of having the voltage at I1 near its crestvalue at the ever, in Fig. 3 I haveinserted some series react ance inthe form of an inductance element 40 in circuit with a resistor element2|. Withthe addition of inductance as at 40, it will be appreciated thatthe circuit consisting of the resistance 2|, the inductance 40, and thestray capacitance from point I9 to ground, having both inductance andcapacitance, may be oscillatory and if a large value of inductance isintroduced at 40 and an appreciable change of current suddenly impressedon the circuit at l9, this oscillation may reach a very high magnitude.The events taking place at interruption amount substantially to suddenlyimpressing on the circuit a current equal to that flowing at the timethrough the resistance 2| which might easily be sufficient to give riseto an oscillation of very high amplitude. The amplitude of thisoscillation can becontrolled, however, by properly proportioning themagnitude of the inductance 40. It may be shown, for example, that ifthis inductance is made equal to about 3R C where R is the resistance ofthe unit 2| and C is the stray capacimentarilv at quite a low value.

tance at point IS, an overshoot to approximately double the crest valueof the applied voltage will be obtained under ideal conditions. If it isdesired to simulate a circuit condition for comparatively low overshoot,a lower value of inductance would be suitable.

The foregoing arrangement may be found to be quite beneficial inintroducing oscillations and overshoot into the voltage recovery curve,which will cause it to simulate more closely the voltage recoveryconditions associated with a normal operation without serious sacrificein the phase relationship and the recovery rate conditions mentionedabove. This simple feature thus permits elimination of the resistorelement 36 and the spark-gap 31.

I have thus provided a synthetic circuit breaker testing circuit whicheliminates the difliculty of automatically synchronizing the applicationof the recovery voltage with the passage of the current to zero as thecircuit interrupting device being tested is opened. The apparatusautomatically determines very promptly when the current zero hasoccurred, and applies a surge or recovery voltage transient within a fewmicroseconds after that time. In the present arrangement, the recoveryrate may be made quite high since at the time of current zero in thebreaker, current is already established in that part of the circuitwhich supplies the high voltage. While the recovery rate is subject tocertain conditions with reference to the current circuit, the inductanceinvolved here is very low and as a result the recovery rate of thiscircuit may be very high.

It is not necessary that both the auxiliary breaker and the breakerunder test shall have extremely positive interrupt-characteristics. Bythis I refer to the requirement that these breakers will or will notinterrupt at a given current zero regardless of whether the recoveryvoltage resulting is that for which the test is being made or a verymuch lower one. While this requirement is present in some degree in thecircuit of the present invention, its severity is greatly reducedbecause interruption by the breaker under test will in some respectstend to encourage interruption by the auxiliary breaker at the samecurrent zero, and similarly failure of the test breaker to interrupt ata given current zero will encourage failure of the auxiliary breaker tointerrupt at the same current zero. This is explained as follows: Thebreaker under test will always reach its current zero slightly ahead ofthe other breaker and will have initially a higher recovery rate appliedto it, while the voltage across the auxiliary breaker is maintained mo-Should the gap of the test breaker break down, however, a voltage equalto that which the generator circuit has attained after the opening ofthe breakers is immediately thrown across the auxiliary breaker. Duringthe early part of the recovery transient,

this will greatly increase the voltage across theauxiliary breaker andthus tend to favor a break down of its gap, although during the latterpart of the recovery transient, this would of course not be true. Undercertain conditions, therefore, the auxiliary breaker has a tendency toclear its part of the circuit when the test breaker clears, and ,torestrike when the test-breaker restrikes, carrying an additional halfcycle of current at the end of which the circuit will operate in thesame manner as before, and the breaker will have another chance to clearagainst full voltage. This is an extremely valuable characteristic sincethe clearing of the auxiliary breaker either a half cycle before or ahalf cycle after the test breaker vitiates the test.

I have herein shown and particularly described certain embodiments of myinvention and certain methods .of operation embraced therein for thepurpose of explaining its principle and showing its application but itwill be obvious to those skilled in the art that modifications andvariations are possible and I aim, therefore, to cover all suchmodifications and variations as fall within the scope of my inventionwhich is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

I. An arrangement for. testing circuit breaker units comprising incombination with a unit to be tested, an auxiliary circuit breaker unit,a high current source, a high voltage source for applying a simulatedrecovery voltage to the breaker unit under test, a resistance element,means connecting said circuit breaker units in series circuit relationto said high current source, means connecting said resistance elementbetween said high voltage source and the high voltage terminal of thebreaker unit under test, and means associated with the circuit of saidhigh voltage source and said breaker under test whereby the desiredovershoot may be obtained in said recovery voltage.

2. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested an auxiliary circuit breaker unit,a high current source of alternating current, an inductive reactanceelement, means connecting said circuit breaker units and said inductivereactance element in series to said high current source, said inductivereactance element tending to reduce to zero the current through theauxiliary breaker immediately after extinction of the arc in the circuitbreaker unit to be tested, a source of high potential, an impedanceelement, means connecting said impedance element between said highpotential source and the high voltage termi nal of the breaker unitunder test.

3. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested. an auxiliary circuit breaker unit,a

' source of- -relatively high alternating current, a

high voltage terminal of the breaker unit under test.

4. An arrangement for testing circuit breaker units comprisingincombination with a unit to be tested, an auxiliary circuitbreaker unit,a polyphase alternating current generator for providing a high current,a high potential transformer having relatively low and high potentialwindings, an inductive reactance element, means connecting said circuitbreaker units and said reactance element in series circuit realtion withat least one phase of said generator, means connecting the low potentialwinding in circuit with an unused phase of said generator, a phaseshifting device connected to the high potential winding of saidtransformer, an impedance element comprising a resistance unit, meansconnecting said impedance element and a portion of said phase shiftingdevice in series circuit relation across the breaker unit under test,and means associated with the circuit including the br'eaker unit undertest and said phase shifting device for obtaining the desired overshootin the simulated recovery voltage obtained from said phase shiftingdevice.

5. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested, an auxiliary circuit breaker unit,

a high current source of alternating current, an inductive reactanceelement, means connecting said circuit breaker units and said inductivereactive element in series to said high current source, said reactanceelement being connected between said high current source and theterminal of said auxiliary breaker 'unit nearest said current source, asource of high potential, .an impedance element including a resistance,means connecting said impedance element between said high potentialsource and the high voltage terminal of the breaker unit under test.

6. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested, an auxiliary circuit breaker unit,a source of alternating current, said circuit breakerunits beingconnected in series across said current source, a source of relativelyhigh potential alternating current, a phase shifting device connected tosaid source, a resistance element, said Ill necting said circuit breakerunits and said in ductive reactance element in series to said currentsource, said reactance element being connected between said currentsource and the terminal of said auxiliary breaker unit nearestsaidcurrent source, a source of high potential, an impedance phase shiftingdevice including a capacitor, said phase shifting device being connectedto said high potential source, an impedance element, and meansconnecting said impedance element and said capacitor in across thebreaker unit under test.

8. An arrangement for testing circuit-breaker units at rated kilovoltamperes without the expenditure of a corresponding amount of power, saidarrangement comprising in combination with the circuit breaker unit tobe tested, an auxiliary circuit breaker unit, a source of alternatingcurrent, an inductive reactance element, means connecting said circuitbreaker units and said inductive reactance, element in series to saidcurrent source, said reactance element being connected between saidcurrent source and the terminal of said auxiliary breaker unit nearestsaid current source, a source of high potential, said high potentialhaving a leading phase relation with respect to said current source, aresistance element connected between said high potential source and thehigh voltage terminal of the breaker unit under test, asecond resistanceelement and a spark-gap, and means connecting said second resistanceelement and said sparkgap in series across the breaker unit under test.

9. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested, an auxiliary circuit breaker unit,a polyphase alternating current generator for providing a high current,a high potential transformer having relatively low and high potentialwindings, an inductive reactance element, means connecting said circuitbreaker units and said reactance element in series circuit relation withat least one phase of said generator, said reactive element beingconnected between on of said gen,-

erator terminals and the terminal of said auxiliary breaker unit nearestsaid generator, means connecting the low potential winding in circuitwith an unused phase of said generator, a phase shifting deviceconnected to the high potential winding of said transformer, animpedance element comprising a resistance unit, means connecting saidimpedance element and a portion of said phaseshifting device in seriescircuit relation across the breaker unit under test, and

=means associated with the circuit including the breaker unit under testand-said phase shifting device for obtaining the desired overshoot inthe simulated recovery voltage obtained from said phase shifting device.

10. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested an auxiliary circuit breaker unit,a high current source of alternating current, an inductive reactanceelement, means connecting said circuit breaker units and said inductivereactance element in series to said high current source, said reactancevelement being connected between said auxiliary breaker and the breakerunit under test, a source of high potential, an impedance element, meansconnecting said impedance element between said high potential source andthe high voltage terminal of the breaker unit under test.

11. An arrangement for testing circuit-breaker units comprising incombination with a unit to series be tested, an auxiliary circuitbreaker unit, a relatively high current source, a relatively highvoltage source, an impedance element comprising a resistance and aninductance, means connecting said circuit breaker units in seriescircuit relation to said high current source, and means connecting saidimpedance element between said high voltage source and the high voltageterminal of the breaker unit under test.

12. An arrangement for testing circuit breaker units at rated kilovoltamperes without the ex penditure oi a corresponding amount of power,said arrangement comprising in combination with the circuit breaker unitto be tested, an auxiliary circuit breaker unit, a source of alternatingcurrent, an inductive reactance element, means connecting said circuitbreaker units and said inductive reactance element in series to saidcurrent source, said reactive element being connected between saidauxiliary breaker and the breaker unit under test, a source of highpotential, an im-" pedance phase shifting device including a capacitor,said phase shifting device being connected to said high potentialsource, a resistance element, and means connecting said resistanceelement and said capacitor in series across the breaker unit under test.

13. An arrangement for testing circuit breaker units at rated kilovoltamperes without the expenditure of a corresponding amount of power, saidarrangement comprising in combination with the circuit breaker unit tobe tested, an auxiliary circuit breaker unit, a source of alternatingcurrent, an inductive reactance element,

means connecting said circuit breaker units and said inductive reactanceelement in series to said current source, said reactance element beingconnected between said auxiliary breaker and the breaker unit undertest, a source of high potential for applying a simulated recoveryvoltag to the breaker unit under test, said high potential having aleading phase relation with respect to said current source, a resistanceconnected between said high potential source and the high voltageterminal of the breaker unit under test,.

and means associated with the circuit of said high potential'source andsaid breaker under test for causing said recovery voltageinstantaneously to exceed the crest value of the voltage applied fromsaid high potential source.

14. An arrangement for testing circuit breaker units comprising incombination with a unit to be tested, an auxiliary circuit breakerunit,- a polyphase alternating current generator for providing arelatively high alternating current, a high potential transformer havingrelatively low and high potential windings, said breaker units beingconnected in series to at least one phase of said generator, said lowpotentialwinding of said transformer being connected in circuit with anunused phase of said alternator, a phase shifting device connected tothe highpotential winding of said transformer, an impedance deviceincluding an inductance unit and a resistance unit and means connectingsaid impedance device and a portion of said phase shifting device acrossthe breaker unit under test.

WILFRED F. SKEATS.

